Mereo BioPharma Reports Full Year 2022 Financial Results and Recent Highlights London

Mereo BioPharma Reports Full Year 2022 Financial Results and Recent Highlights

March 28, 2023 - Mereo BioPharma Group plc (NASDAQ: MREO) ( Mereo or the Company ), a clinical-stage biopharmaceutical company focused on rare diseases, today announced its financial results for the

year ended December 31, 2022 and provided an update on recent corporate highlights.

In 2022, we made important progress in the

ongoing advancement of our core rare disease programs. The data from our Phase 2 ASTRAEUS study of alvelestat in severe alpha-1-antitrypsin deficiency-associated lung

disease (AATD-LD) were highly encouraging, and formed the basis for productive discussions with the regulatory agencies in both the U.S. and EU, culminating in our recent announcement of the details of our

potential pivotal study design, said Dr. Denise Scots-Knight, Chief Executive Officer of Mereo. We believe our discussions with the regulatory agencies reflect the major unmet need for improved therapeutic options for these

patients, and we expect that having this clear path to potential full U.S. and EU approvals based on guidance from both the FDA and EMA will support our ongoing partnering efforts. For our lead rare disease program, our partner Ultragenyx has

continued to advance the development of setrusumab (UX143) for the treatment of osteogenesis imperfecta (OI), with completion of enrollment in the Phase 2 portion of the Phase 2/3 Orbit study in pediatric and adult patients and data is expected in mid-2023. Further, a study in younger pediatric patients is expected to initiate during the first half of 2023. We concluded 2022 with cash and short-term deposits of $68.2 million ( 56.3 million) and

maintain our expectation that we have sufficient runway to fund operations into 2026.

Highlights from 2022, Recent Developments and Anticipated

Alvelestat (MPH-966)

Etigilimab (MPH-313)

Navicixizumab (OMP305B83)

Full Year 2022 Financial Results

Full year 2022 research and development expenses were 25.0 million, compared to 23.6 million, in 2021, an

increase of 1.4 million, or 6%. R&D expenses relating to etigilimab increased by 2.3 million. The increase was due to the costs associated with additional patients and the duration of treatment for patients responding to

therapy in 2022 compared to 2021 in the open label Phase 1b/2 basket study in combination with an anti-PD-1 in a range of tumor types. R&D expenses relating to

alvelestat increased 0.1 million, or 2%, primarily reflecting the end of study related costs for the Phase 2 proof-of-concept study in AATD. Partially

offsetting the increases, R&D expenses relating to setrusumab decreased by 0.2 million, or 7%. Setrusumab R&D expenditure in 2022 comprised activities associated with laying the groundwork for reimbursement discussions in Europe,

and input into development, regulatory and manufacturing plans with our partner, Ultragenyx, as the global development of the program is funded by Ultragenyx pursuant to our licensing and collaboration agreement.

Administrative expenses increased by 3.6 million, or 23%, from 15.9 million in 2021 to 19.5 million in

2022. The increase was primarily driven by additional costs incurred in connection with the Schedule 13D filings and subsequent Cooperation Agreement with Rubric Capital, and increased share-based payment expenses, partially offset by a reduction in

other professional fees.

Net loss attributable to equity holders for the year ended December 31, 2022 was 34.2 million,

compared to a net profit of 12.7 million in 2021, primarily reflecting an operating loss of 43.6 million and a gain of 7.8 million due to changes in the fair value of financial instruments resulting from an

unrealized gain on warrants.

As of December 31, 2022, the Company had cash and short-term deposits of 56.3 million

($68.2 million). Net cash burn during the fourth quarter of 2022 amounted to 11.2 million ($13.5 million). The Company expects its existing cash and short-term deposits will enable it to fund its currently committed clinical trials,

operating expenses and capital expenditure requirements into 2026.

Total ordinary shares outstanding at December 31, 2022 were

approximately 625 million. Total ADSs outstanding at December 31, 2022 were approximately 119 million, with each ADS representing five ordinary shares of the Company.

About Mereo BioPharma

Mereo BioPharma is a biopharmaceutical company focused on the development of innovative therapeutics for rare diseases. The Company has

developed a robust portfolio of clinical stage product candidates. The Company has two rare disease product candidates, setrusumab for the treatment of osteogenesis imperfecta (OI) and alvelestat for the treatment of severe alpha-1-antitrypsin deficiency-associated lung disease (AATD-LD) and Bronchiolitis Obliterans Syndrome (BOS). The Company s

partner, Ultragenyx Pharmaceutical, Inc., has initiated a pivotal Phase 2/3 pediatric study in young adults (5-25 years old) for setrusumab in OI and expects to initiate a study in pediatric patients (<5

years old) in the first half of 2023. The partnership with Ultragenyx includes potential milestone payments of up to $254 million and royalties to Mereo on commercial sales in Ultragenyx territories. Mereo has retained EU and UK commercial

rights and will pay Ultragenyx royalties on commercial sales in those territories. Alvelestat has received U.S. Orphan Drug Designation for the treatment of AATD, Fast Track designation from the FDA, and positive data were reported from a Phase 2 proof-of-concept study in North America, Europe and the UK. In addition to the rare disease programs, Mereo has two oncology product candidates in clinical development.

Etigilimab (anti-TIGIT) has completed enrollment in a Phase 1b/2 basket study evaluating its safety and efficacy in combination with an anti-PD-1 in a range of tumor

types including three rare tumors and three gynecological carcinomas cervical, ovarian, and endometrial; Navicixizumab, for the treatment of late line ovarian cancer, has completed a Phase 1 study and has been partnered with OncXerna

Therapeutics, Inc. in a global licensing agreement that includes payments of up to $300 million in milestones and royalties.

This press release contains forward-looking statements, including the Company s expectations regarding its

proposed Phase 3 study evaluating a single dose of alvelestat versus placebo, the expectations regarding a study in pediatric patients evaluating setrusumab, and the Company s pipeline of product candidates. All statements other than statements

of historical fact contained in this press release are forward-looking statements within the meaning of Section 27A of the U.S Securities Act of 1933, as amended, and Section 21E of the U.S Securities Exchange Act of 1934, as amended.

Forward-looking statements usually relate to future events and anticipated revenues, earnings, cash flows or other aspects of our operations or operating results. Forward-looking statements are often identified by the words believe,

expect, anticipate, plan, intend, foresee, should, would, could, may, estimate, outlook and similar expressions,

including the negative thereof. The absence of these words, however, does not mean that the statements are not forward-looking. These forward-looking statements are based on the Company s current expectations, beliefs and assumptions concerning

future developments and business conditions and their potential effect on the Company. While management believes that these forward-looking statements are reasonable as and when made, there can be no assurance that future developments affecting the

Company will be those that it anticipates. All of the Company s forward-looking statements involve known and unknown risks and uncertainties some of which are significant or beyond its control and assumptions that could cause actual results to

differ materially from the Company s historical experience and its present expectations or projections. Such risks and uncertainties include, among others, the uncertainties inherent in the clinical development process; the Company s

reliance on third parties to conduct and provide funding for its clinical trials; the Company s dependence on enrollment of patients in its clinical trials; and the Company s dependence on its key executives. You should carefully consider

the foregoing factors and the other risks and uncertainties that affect the Company s business, including those described in the Risk Factors section of its latest Annual Report on Form 20-F,

reports on Form 6-K and other documents furnished or filed from time to time by the Company with the Securities and Exchange Commission. The Company wishes to caution you not to place undue reliance on any

forward-looking statements, which speak only as of the date hereof. The Company undertakes no obligation to publicly update or revise any of our forward-looking statements after the date they are made, whether as a result of new information, future

events or otherwise, except to the extent required by law.

Consolidated Statements of Comprehensive (Loss)/Income

Consolidated Balance Sheets